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  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>这是我的网页</title>
  <style>
    div {
      width: 0;
      height: 0;
      border-left: 50px solid transparent;
      border-right: 50px solid transparent;
      border-bottom: 100px solid red;
    }
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<body>
  <h1>Hello YK菌</h1>
  <h2>感谢字节，感谢开课吧，感谢各位老师 YYDS</h2>
  <h3>别的我也不会，那我就给各位画一个三角形吧</h3>
  <div></div>
  <img src="YKjun.jpg" alt="" width="300px" />
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